Rolling bearings are widely used in various mechanical applications, including the automotive field. Tandem rolling bearings include two rows of rolling elements. The two rows are arranged in a stepped-manner, axially offset in relation to one another. These rows generally include cages for retaining and separating the rolling elements in the circumferential direction. A subset of this is tandem ball bearings where the rolling elements are balls. Tandem ball bearing assemblies can include a small and large rolling element subassembly. Each subassembly includes a cage and a plurality of the rolling elements. Retention of the rolling element subassemblies depends on the diametrical interference between the retention diameter of the smaller rolling element subassembly, defined as the diameter formed on the radially inner surface of the rolling elements, and the diameter of a retention element formed on an axial end of the inner ring. Slight deviations of the retention diameter of the smaller rolling element subassembly, due to geometric tolerances, moisture absorption, and/or thermal expansion, can cause excessive or inadequate retention of the smaller rolling element subassembly on the inner ring.
Cages for separating rolling elements are typically made from plastic in an injection-molding process. U.S. Patent Application 2010/0189386 A1 discloses an angular-contact ball bearing in a tandem arrangement. The two main types of cages currently used in rolling bearing assemblies are closed and open. Closed cages retain rolling elements in the circumferential direction and both axial directions. When installed in a bearing assembly, the rolling elements arranged in a closed cage are retained about a given axis by either the cage or the races of the rings. U.S. Pat. No. 6,783,279 B2 discloses a closed cage tandem rolling bearing where closed cages retain the rolling elements. These closed cages require additional space between the rolling element subassemblies to maintain necessary clearance during operation. Because of their configuration, closed cages are often stiffer than similarly sized open cages. As a result, closed cages are more sensitive with respect to their retention properties than open cages, and the retention forces provided by closed cages are greater than open cages.
Open cages separate rolling elements in the circumferential direction and retain the rolling elements on one axial side. U.S. Patent Application 2010/0296761 A1 discloses an open cage tandem rolling bearing. These open cages do not retain rolling elements in the outer radial direction and both axial directions.
Providing retention of the rolling elements in the outer radial direction as well as in the axial directions would be desirable during installation of cage subassemblies onto an inner ring of a bearing assembly.
It would also be desirable to retain the rolling elements in the cages during the installation of the subassemblies onto the outer ring. After the rolling element subassemblies are secured on the inner ring, this inner ring subassembly is dropped a short distance down a shaft with the smaller rolling element subassembly facing down. The inner ring subassembly comes to rest at an intermediate position before being pressed into position with the outer ring. Retention of the smaller rolling element subassembly on the seat of the smaller race of the inner ring during installation is necessary.
Therefore, a need exists for a tandem rolling bearing having the advantages of both the open and closed cages. A need exists for a cage for a tandem rolling bearing that does not have the increased width requirements or stiffness provided by the closed cages that still provides improved retention of the rolling elements during assembly.